Carbon particles coated with polymer films, methods for their production and uses thereof

ABSTRACT

The present disclosure relates to a composition comprising plasma coated fullerenic soot particles, methods for the preparation thereof, and its use in polymer blends.

This application is a divisional application of U.S. application Ser.No. 13/123,426, filed on Oct. 24, 2011, which is a U.S. national stageentry under 35 U.S.C. § 371 from PCT International Application No.PCT/EP2009/063211 filed Oct. 9, 2009, and claims priority to and thebenefit to the filing date of EP Application No. 08166358.5, filed Oct.10, 2008, all of which are incorporated herein by reference.

SUMMARY OF THE INVENTION

The present invention relates to a composition comprising plasma coatedfullerenic soot particles, methods for the preparation thereof, andtheir use in polymer blends.

BACKGROUND OF THE INVENTION

Carbon black is used as conductive additive to polymers, thermoplasticsand rubbers. Polymer/carbon black composites usually show a very typicalpercolation behavior. The electrical resistivity of the compositefollows a curve as shown in FIG. 1.

As illustrated in FIG. 1, the addition of carbon black to a polymercomposition is, up to a certain level, without any effect on the DCresistivity, then suddenly the resistivity drops to a low level andevolves further only very slowly, which is well-known phenomenon in theart. The influence of the type of carbon black chosen as a filler istypically only on the concentration needed to achieve the percolationeffect, while the resulting resistivity of the polymer/carbon blackblend remains at a constant level, regardless of the type of carbonblack added as a filler. In some applications, a conductive polymer is,however, not desirable, and the filler should only be used as anantistatic modifier to nonconductive polymers.

Carbon black is also commonly employed as a filler in elastomer (rubber)blends. Such Rubber blends have a great importance in, e.g., the tireindustry. Since different rubbers have different types of responses tostress, blending of selected rubbers has been practiced to meet the needof the contradictory set of properties, i.e. yielding rubber productswith the desired properties. Blending also improves the processabilityof rubbers and may overall reduce costs of production.

Rubbers are hardly used in their pure form. They are commonly mixed withreinforcing fillers, non-reinforcing fillers, plasticizers, processaids, antioxidants and vulcanization ingredients to provide the requiredphysical properties and to bring about an optimum level ofvulcanization. In contrast, thermoplastics are mixed with fewingredients such as fillers, stabilizers and process aids and areprocessed at a temperature above their melting point or glass transitiontemperature.

In fact, carbon black is one of the most important active fillers usedin the rubber industry for improving the mechanical and dynamicproperties of rubbers. The behavior of these fillers in rubber matricesis very different, mainly because of the difference in their surfacecharacteristics. The surface characteristics of the filler have animportant contribution towards the wetting behavior, interaction withthe rubber matrix, reagglomeration in the matrix, etc.

One problem commonly encountered with carbon black fillers is that thesurface energy of conventional carbon black is normally higher than thatof various elastomers like Styrene-Butadiene rubber (SBR), Butadienerubber (BR), and Ethylene-Propylene-Diene rubber (EPDM). With a largesurface energy difference between filler and rubber, the filler-fillerinteraction increases, which in turn has a negative influence on thestability of the dispersion state attained during mixing. Reducing thesurface energy and chemistry to the range of various rubbers may aid incompatibilizing these fillers.

In order to modify the surface energy and properties of the carbon blackparticles, attempts have been made to coat the carbon black particleswith a polymer layer. The creation of a polymer film on the surfaceresults in an altered contact resistance and contact capacity. In otherwords, polymer/carbon black blends employing polymer coated carbon blackshow an increased DC resistivity compared to polymers or blends withnon-modified carbon black fillers because the electrons will have totunnel through the additional surface polymer layer of the particle tointeract with the surrounding filler particles or polymers.

Surface modification of carbon black by polymerization is generallyknown in the art. Polymerization of carbon black by conventionalpolymerization reactions (dissolving the monomer in a suitable solvent,contacting the monomer solution and possible additives with the carbonblack particles and subsequent evaporation of the solvent (mostly byheating) to form a polymer layer on the surface of the particles) hasbeen described in the art. For example, depositing epoxy or phenolresins onto the surface of fullerenic soot containing carbon black inthe presence of solvents is described in Japanese Published UnexaminedApplication No. 1996-291295 (JP 08 291295 A) to Tokai Carbon KK.

Conventional polymerization has, however, a number of disadvantages,such as the requirement to apply heat to achieve the immobilization ofthe layer on the surface, and the unwanted presence of residual solventsor of other additives used to accomplish the polymerization in the finalproduct.

Plasma polymerization has emerged as a surface modification techniquefor metals, polymers and powders. Plasma polymerization is differentfrom the conventional polymerization processes. The polymer formed fromplasma polymerization and conventional polymerization generally differwidely in chemical composition, as well as chemical and physicalproperties, even if the same monomers are used for polymerization. Thisuniqueness of plasma polymers results from the reaction mechanism of thepolymer forming process.

The technique involves electric field bombardment of monomer molecules,thereby creating active monomer species, which then react with thesurface to form a film on the substrate. As a result, the surfaceproperties of the substrate change dramatically. By suitable selectionof monomers, a substrate can either be made hydrophobic or hydrophilic.Plasma polymerization can be carried out at ambient temperature and doesnot require any solvents for the process, making it a clean process.

The surface of carbon black is known to consist of graphitic planes(site I), amorphous carbon (site II), crystallite edges (site III), andslit shaped cavities (site IV). The conduction electrons associated withthe graphitic structure play an important role in the amount of energyassociated with these sites. Recently, Schroder et al. [1] quantifiedthe different energies at these sites on the surface of carbon black byanalyzing adsorption isotherms of various molecules. According to theiranalysis, particularly the crystallite edges (III) and slit shapedcavities (IV) on the surface of carbon black are the sites of highconcentration of π-electrons (see FIG. 2). These sites are mostimportant with respect to rubber-filler and filler-filler interaction.The conduction electrons associated with the graphitic structure play animportant role in the amount of energy associated with these sites.

Furthermore, the surface of carbon black is also covered with functionalgroups like carboxyl, phenol, lactones and quinonic groups (see FIG. 3).These are preferably located at the edges of the graphitic basal planesor at the crystallite edges.

When carbon black is exposed to plasma, the following processes canoccur:

C—C bond breakage in the graphitic planes.

Due to breakage of these C—C bonds, radicals are generated on thegraphitic planes. However, the graphitic structures are stabilized byresonance. As soon as radicals are generated, they will reform the bondand return to their stable state.

The breakage of C—O bonds and other functional groups, located at thecrystallite edges. As soon as a C—O bond or another functional grouplocated at the crystallite edges is broken, monomer active species canattach on to these sites, which is more favourable.

Successful attachment of the monomer active species only happens at thesites generated at the crystallite edges, i.e., at the sites generatedby the bond breakage of the functional groups. For furnace carbonblacks, the concentration of these active sites (II-IV) varies between5-20% on the surface, and the other 95-80% contribution is fromgraphitic planes. Furnace carbon blacks with higher surface area andlower particle size has more fractions of these energetic sites (sitesII-IV). As the surface area decreases and particle size increases andthe fraction of these sites decreases.

The extension of plasma polymerization as a surface modificationtechnique for fillers like carbon black and silica for application inrubber evolved quite recently. Nah et al. [2] reported plasmapolymerization on silica and its effect on rubber properties. Akovali etal [3]. and Tricas et al [4,5] reported the modification of carbon blackby plasma polymerization. The monomers used for the process were acrylicacid, styrene and butadiene. Their findings led to the conclusion thatcarbon black was modified successfully, with the coating covering allsites on the surface of carbon black. Kang et al, [6] also reported onthe modification of carbon black by plasma polymerization and concludedthat it is possible to manipulate the surface properties.

However, it was found that not all types of carbon black can besuccessfully subjected to plasma polymerization, and that most carbonblacks are coated only with very low amounts of plasma polymer comparedto silica, leading to insufficient changes of their surface properties(see, for example, Mathew et al. [7]). Other problems observed were lowuniformity of the plasma polymer coated particles, long treatment timesand poor reproducibility for various types of carbon black.

LITERATURE REFERENCES

-   [1] A. Schroder, PhD Thesis, University of Hannover, Deutsches    Institut für Kautschuktechnologie, Hannover Germany, (2000)-   [2] C. Nah, M. Y. Huh, J. M. Rhee, and T. H. Yoon, Polym. Int. 51,    510, (2002)-   [3] G. Akovali and I. Ukem, Polymer 40, 7417 (1999)-   [4] N. Tricas, E. Vidal-Escales, S. Borros, and M. Gerspacher, 16th    Conference of International Society of Plasma Chemistry, Taormina,    Italy (2003)-   [5] N. Tricas, S. Borros and R. H. Schuster, Proceedings of the    Kautschuk-Herbst-Kolloquium, Hannover Germany, (2004)-   [6] Y. C. Kang and W. J. van Ooij, Proceedings ACS Rubber Div. Fall    Meeting, Cincinnati, Paper 67 (2006)-   [7] T. Mathews, R. N. Datta, W. K. Dierkes, J. W. M.    Noordermeer, W. J. van Ooij, Plasma Chem Plasma Process, 28, 273-287    (2008)

Having regard to the state of the art, there remains a need for surfacemodified carbon black compositions that can be successfully andreproducibly prepared by plasma polymerization techniques.

SUMMARY OF THE INVENTION

The inventors have now surprisingly found that when carbon particles offullerenic soot are employed in a plasma polymerization process, theprocess can be carried out reliably and with good efficiency, resultingin plasma polymerized carbon black composition having advantageousproperties over products obtained through conventional polymerizationtechniques. Furthermore, it has been found that a modification of theplasma polymerization conditions allows properties such asresistivity/conductivity of the product to be adjusted to achieve a widerange of desired properties of the compositions. In the context of thepresent invention, such compositions are referred to as plasma coatedfullerene soot or PCFS.

In one embodiment, the present invention provides a compositioncomprising carbon particles of fullerenic soot, characterized in thatthe carbon particles of fullerenic soot carry a coating of a layerconsisting of a plasma polymerized monomer on a core carbon particle.

In certain embodiments, the PCFS composition is characterized in thatthe layer of polymerized monomer represents 1.0-30%, preferably 1.5-20%,or more preferably 1.5-8.0% of the mass of the particle. The mass of thepolymerized monomer layer is conveniently determined bythermogravimetric analysis.

In further embodiments, the PCFS composition is characterized in thatthe surface energy of the carbon particles is less than 65.0 mJ/m², orless than 60.0 mJ/m², or less than 57.0 mJ/m². In other embodiments, thePCFS composition is characterized in that the electrical resistivitythereof is higher than 0.4 Ohm, cm.

In yet further embodiments, the PCFS composition is characterized inthat the core carbon particles are fullerene soot particles produced byhigh temperature plasma using graphite or other carbon allotropes asprecursor. In other embodiments, the composition is characterized inthat the core carbon particles are fullerene soot particles produced byradio frequency (RF) plasma using carbon black, graphite or other carbonallotropes as precursor. Alternatively, the core carbon particles arefullerene soot particles produced by a combustion process or by an arcprocess or laser ablation.

In certain embodiments, the layer of polymerized monomer consists of apolymerized hydrocarbon monomer, where the monomer comprises at leastone carbon-carbon double bond. In a specific embodiment, the monomer isacetylene.

The PCFS compositions of the present invention are obtainable by aprocess of plasma polymerization of the monomer on the surface of thecore carbon particles of fullerenic soot.

Thus, another aspect of the present invention is the provision of aprocess for the preparation of a PCFS composition as described above,characterized by carrying out a plasma polymerization of the monomer onthe core carbon particle of fullerenic soot in a plasma polymerizationreactor.

In yet another aspect of the invention, blends are provided comprising aPCFS composition as described above, and one or more polymers. Incertain embodiments, the polymer is a natural or synthetic elastomer,preferably selected from the group consisting of natural rubber,styrene-butadiene-rubber, acrylonitrile-butadiene-rubber, orethylene-propylene-diene rubber.

In certain embodiments of this aspect of the invention, the blend ischaracterized in that the ultimate resistivity is within the rangebetween 103 and 1013 Ohm·cm. In any event, the blends comprising a PCFScomposition as provided by the present invention are characterized by ahigher resistivity compared to compositions containing non-polymerizedcarbon particles, even with otherwise similar components.

In yet another aspect of the present invention, the plasma coatedfullerenic soot in the blend is used to compatibilize polymers with lowaffinity to each other and differing affinity to the carbon filler.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows the electrical resistivity curve of polymer/carbon blackcomposite.

FIG. 2 shows the attribution of energy sites I-IV to carbon blackmicrostructures.

FIG. 3 shows functional groups on the surface of carbon black.

FIG. 4 shows a schematic representation of a vertical plasma reactorsuitable for the processes of the present invention.

FIG. 5A shows the TGA thermograms of E-250g & E-250g Ac carbon particlesbefore and after plasma polymerization of acetylene on the surfacethereof.

FIG. 5B shows the TGA thermograms of E-MM131 & E-MM131 Ac carbonparticles before and after plasma polymerization of acetylene on thesurface thereof.

FIG. 5C shows the TGA thermograms of E-P434& E-P434 Ac carbon particlesbefore and after plasma polymerization of acetylene on the surfacethereof.

FIG. 5D shows the TGA thermograms of RP-P534 & RP-P534 Ac carbonparticles before and after plasma polymerization of acetylene on thesurface thereof.

FIG. 5E shows the TGA thermograms of KS4 & KS4 Ac carbon particlesbefore and after plasma polymerization of acetylene on the surfacethereof.

FIG. 5F shows the TGA thermograms of E-P434 & E-P434 Ac-5 carbonparticles before and after plasma polymerization of acetylene on thesurface thereof.

FIG. 6 shows resistivities of coated versus uncoated fullerenic sootsamples.

FIG. 7 shows the Payne effect in SBR at various fullerenic sootloadings.

FIG. 8 shows the Payne effect in NBR at various fullerenic sootloadings.

FIG. 9 shows the Payne effect in EPDM at various fullerenic sootloadings.

FIG. 10 shows percentage reduction of the Payne effect in differentrubbers.

FIG. 11 shows the stress-strain curve of SBR with 40 phr plasma-coatedfullerenic soot.

FIG. 12 shows the stress-strain curve of NBR with 40 phr plasma-coatedfullerenic soot.

FIG. 13 shows the stress-strain curve of EPDM with 40 phr plasma-coatedfullerenic soot.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

One of the aims of the present invention is to provide a reliable andconvenient process to modify the surface of carbon particles by a plasmapolymerization process in order to deposit a polymeric layer on itssurface for applications in a variety of applications, includingantistatic nonconductive polymers or rubber and rubber blends. Thetechnique involves plasma polymerization which involves electric fieldbombardment of monomer molecules, thereby creating active monomerspecies, which then react with the surface of the carbon particles offullerenic soot (FS) to form a film over the substrate. As a result ofthis modification, the surface properties of the FS substrate changedramatically. By selecting suitable monomers, a substrate can either bemade hydrophobic or hydrophilic. The PCFS compositions obtained by theprocess of the present invention can be used, for instance, as a fillerin tires.

Surprisingly, it has been found that when fullerenic soot carbonparticles are used in the plasma polymerization process, the changes inthe surface properties of the compositions can be achieved faster thanobserved for conventional carbon black particles. For example, acomposition comprising conventional carbon black particles requires afour hours treatment in an acetylene plasma to reach the same value ofsurface tension obtained with a fullerenic soot carbon particlecomposition in an acetylene plasma for one hour (see Example 2).

Fullerenic Soot

The term “fullerenic soot” as used herein is to be understood equivalentto “carbon containing residue from fullerene production and carbonnanostructures production”, and means a residue which comprises asubstantial proportion of fullerene-type nanostructures. The proportionof fullerene-type carbon compounds is determined via the presence of 5-or 6-membered carbon rings which lead to curved layers of carbon on thecarbon black surface. The proportion of fullerene-type carbonnanostructures here is usually approximately 100%, but can be less. Thedecisive factor is the requirement to permit functionalization whichbrings about a significant change in the properties of the carbon black.The proportion is preferably from 80% to 100%. This preferred proportioncan change with the application, however.

In principle, any of the known processes for fullerene production and/orcarbon-nanostructures production is suitable for obtaining thecarbon-containing residue.

Furnace blacks or carbon blacks from other processes are also suitableas long as the fullerene-type residues on the surface are present.

According to one preferred embodiment, the carbon-containing residue isobtained via ablation of a carbon electrode by means of an electric arc,a laser, or solar energy. A process for electric arc ablation isdescribed by Journet, C. et al., Nature 388 (1997), 756. A processsuitable for laser ablation of carbon and production of acarbon-containing residue is for example described in Thess, A. et al.,Science 273 (1996), 483. A process suitable for production ofcarbon-containing residue via chemical vapor deposition usinghydrocarbons is furthermore described in Ivanov et al., Chem Phys. Lett.223, 329 (1994). Another production process using plasma technology isdescribed in Taiwanese Patent Application No. 93107706 and a suitablesolar energy process for the production of a carbon-containing residueis described in Fields et al., U.S. Pat. No. 6,077,401.

The carbon-containing residue can be obtained via incomplete combustionof hydrocarbons. By way of example, fullerene production has beenobserved in flames derived from premixed benzene/acetylene (Baum et al.,Ber. Bunsenges, Phys. Chem. 96 (1992), 841-847). Other examples ofhydrocarbons suitable for combustion for the production of acarbon-containing residue are ethylene, toluene, propylene, butylene,naphthalene or other polycyclic aromatic hydrocarbons, in particularpetroleum, heavy oil and tar, and these can likewise be used. It is alsopossible to use materials which are derived from carbon, from carrageenand from biomass and which mainly comprise hydrocarbons. However, theycan also comprise other elements, such as nitrogen, sulphur and oxygen.U.S. Pat. No. 5,985,232 describes a particularly preferred process forcombustion of hydrocarbons.

According to another embodiment, the carbon-containing residue can beobtained via treatment of carbon powder in a thermal plasma alongsidefullerenes. As an alternative, the carbon-containing residue can beobtained via recondensation of carbon in an inert or at least to someextent inert atmosphere.

By way of example, EP 0 682 561 A1 describes a process for theconversion of carbon in a plasma gas. Fullerenes, and also carbonnanotubes, can likewise be produced via this process.

The carbon-containing residue is preferably produced via the followingsteps, preferably in this sequence:

-   -   A plasma is generated with electrical energy.    -   A carbon precursor and/or one or more catalysts and a carrier        plasma gas are introduced into a reaction zone. This reaction        zone is, if appropriate, in an airtight vessel that withstands        high temperatures.    -   The carbon precursor is to some extent vaporized at very high        temperatures in this vessel, preferably at a temperature of        4000° C. or higher.    -   The carrier plasma gas, the vaporized carbon precursor and the        catalyst are passed through a nozzle whose diameter narrows,        widens, or else remains constant in the direction of the plasma        gas flow.    -   The carrier plasma gas, the vaporized carbon precursor and the        catalyst are passed through the nozzle into a quenching zone for        nucleation, growth and quenching. This quenching zone is        operated with flow conditions produced via aerodynamic and        electromagnetic forces, so as to prevent any noticeable return        of starting material or products from the quenching zone into        the reaction zone.    -   The gas temperature in the quenching zone is controlled at from        about 4000° C. in the upper part of this zone to about 800° C.        in the lower part of this zone.    -   The carbon precursor used can be a solid carbon material which        involves one or more of the following materials: carbon black,        acetylene black, thermal black, graphite, coke, plasma carbon        nanostructures, pyrolitic carbon, carbon aerogel, activated        carbon or any desired other solid carbon material.    -   As an alternative, the carbon precursor used can be a        hydrocarbon, preferably composed of one or more of the        following: methane, ethane, ethylene, acetylene, propane,        propylene, heavy oil, waste oil, or of pyrolysis fuel oil or of        any other desired liquid carbon material. The carbon precursor        can also be any organic molecule, for example vegetable fats,        such as rapeseed oil.    -   The gas which produces a carbon precursor and/or produces the        plasma involves and is composed of one or more of the following        gases: hydrogen, nitrogen, argon, helium, or any desired other        pure gas without carbon affinity, preferably oxygen-free.

With respect to other process variants, reference is made to WO04/083119, the disclosure content of which is incorporated herein byreference in its entirety.

In preferred embodiments, the carbon precursor is selected from carbonblack, graphite, another carbon allotrope or a mixture thereof.

Alternatively, functionalized fullerenic soots may be used for thepurpose of the present invention. It is known, e.g., from InternationalPatent Application WO 2006/114419 that a functionalization reaction canbe carried out during or after the production process of fullerenicsoot, and the functionalized fullerenic soots obtained thereby are alsoencompassed by the term “fullerenic soot” as used herein.

The functionalization reactions here involve one or more of thefollowing reactions:

-   -   Hydroxylation of the residue, preferably via an oxidant, the        oxidant particularly preferably being potassium permanganate.    -   Reaction of the residue with ammonia, obtaining amino groups.    -   Reaction of the residue with alkyl- or arylamines.    -   Reaction of the residue with ozone, forming ozonides and        subsequently forming carbonyl compounds.    -   Treatment of the residue with a halogenating agent, the        halogenating agent preferably being chlorine or bromine.    -   Subjection of the residue to a cycloaddition reaction,    -   Subjection of the residue to a Grignard reaction,    -   Hydrogenation of the residue.    -   Subjection of the residue to an electrochemical reaction.    -   Subjection of the residue to a Diels-Alder reaction.    -   Formation of donor-acceptor molecule complexes.

Other functionalization reactions suitable alongside the abovementionedreactions are any of those known from the prior art in connection withfullerenes.

Process of Plasma Polymerization

Generally, plasma polymerization according to the present invention canbe carried out in any suitable plasma reactor. Various types of plasmareactors are known to the skilled person. In one embodiment of theinvention, the plasma polymerization is performed in a radio frequency(RE) plasma vertical reactor. A schematic representation of this reactoris shown in FIG. 4.

In a specific embodiment, the reactor consists of a round bottom flaskattached with a long tubular region. Plasma is generated with the helpof a 13.56 MHz Radio frequency (RF) plasma generator (MKS-ENI ACG 3B).Typically, a power output of 80-250 watts is used, (see Table I and V).This is connected to an automatic impedance matching unit (MKS MWH-5)which in turn is connected to a copper coil wound on to the long tubularregion of the reactor. The powders are kept at the bottom of the chamberand stirred with the help of a magnetic stirrer in order to expose thepowder particles uniformly to plasma. The system is evacuated to apressure of 30 mTorr. The monomer is injected into the reaction chamberunder steady flow conditions. The monomer flow is monitored by a massflow controller (MKS-1179A) and the system pressure is monitored by atemperature regulated capacitance manometer (MKS-627B). As the desiredmonomer pressure is attained RF power is applied.

The RF thermal plasma technology for the production of fullerene soot isdescribed, e.g., in Tororovic-Markovic B., Markovic S., Mohai I., KarolyZ., Gal L., Foglein K., Szabo P. I., Szepvoglyi J.; Chemical Phys.Letters, 2003, vol. 378, no 3-4, pp. 434-439.

In the plasma polymerization process, monomer molecules gain high energyfrom electrons, ions, and radicals and are fragmented into activatedsmall fragments, in some cases into atoms. These activated fragments arerecombined, sometimes accompanying rearrangement, and the molecules growto large-molecular weight ones in a gas phase or at the surface ofsubstrates. The repetition of activation, fragmentation, andrecombination leads to polymer formation. In conventional polymerizationthe monomer molecules are linked together through chemical reactionswithout any alteration of chemical structure of the monomer. Thereforethe chemical structure of the polymer formed by conventionalpolymerization is well predicted by the structure of the monomer. Incontrast, in the case of plasma polymerization, the structure of thepolymer is cannot be clearly predicted from the structure of monomers.

In an extreme case, the starting molecule is fragmented into atoms andrestructured into large molecules. Thus, the sequence and chemicalstructure of the formed polymer chains is not identical to that of thestarting molecule. How the starting molecules are fragmented intoactivated small fragments depends on the level of plasma and the natureof the starting molecules. This is a reason why the plasma polymerspossess different chemical composition when the plasma polymerization isoperated at different conditions such as monomer flow rate, radiofrequency (RF) power and pressure of the reaction chamber, even if thesame starting materials are used for the plasma polymerization.

Upon modifying the carbon particles by plasma polymerization, across-linked polymeric film is formed on the surface. A plasma polymerwill contain an appreciable amount of trapped radicals, and uponexposure to atmospheric conditions after the polymerization process, theplasma polymer can easily get oxidized—giving rise to the presence ofoxygen on the surface. The respective concentrations of carbon andoxygen on the surface of the coating can be easily determined by x-rayphotoelectron spectroscopy.

The classes of monomers most commonly encountered in plasmapolymerization are:

1. Hydrocarbons

These need not contain conventionally polymerizable groups. Typicalexamples include acetylene, ethylene, ethane, methane, cyclohexane,benzene, styrene and butadiene. However there will be differencesbetween the performances of these monomers. Polymerization will proceedslower in the case of saturated systems. Also in the case of ethylene,the window under which plasma polymerization can be carried out is verynarrow. Outside this region, there could be the formation of plasmapolymer powder or an oily film.

2. Hydrocarbons with Polar Groups

These may be used to form a more polar plasma polymer. Monomers such asacrylic acid, allyl amine, pyridine, vinyl pyridine, allyl alcohol etcare used for this purpose.

3. Hydrocarbons with Hetero-Molecules,

Monomers such as pyrrole, thiophene, furan can be used.

4. Fluorocarbons

Typical monomer used include perfluorohexane, octafluorotoluene, sulphurhexafluoride, tetrafluoroethylene are used.

5. Silicon Containing Monomers

This includes tetramethylsilane (TMS), tetraethoxysilane (TEOS),hexamethyldisiloxane (HMDSO) etc.

The selection of the monomers always depends on the type of the plasmapolymer required and the practical feasibility of the polymerizationprocess. In general, all of the above-mentioned monomers arecontemplated in the context of the present invention.

Some Advantages of Plasma Polymerization of Carbon Particles

1. Very thin uniform films capable of modifying the surface propertiesof the carbon particles can be generated. For fullerenic soot this istypically in the range of 3-9 nm on a core carbon particle (see Example1).

2. The process is highly versatile since both, a variety of differentmonomers and different reactor conditions can be applied in order toachieve a specific surface property.

3, Since no solvent or catalyst is required for the polymerization, itis possible to form a layer of polymerized monomer having no impuritiesderived from the solvent or a catalyst.

4. Plasma polymerization can be carried out at ambient temperature. Forexample, a radio frequency (RF) plasma vertical reactor can be usedwhich is operated at a typical power output of 80-250 watts (see Table Iand V).

In summary, the surface modification of fullerenic soot obtained by aconventional polymerization process is very different from the chemicalmodification achieved by plasma polymerization. Accordingly, the presentinvention describes processes capable of achieving surface modificationsof fullerenic soot which could not have been achieved with conventionalpolymerization.

To the best of applicants knowledge, processes for modifying fullerenicsoot by plasma polymerization has not been described in the prior art.Of course, the same is true for the PCFS compositions obtainable by thisprocess.

EXAMPLES Example 1: Plasma Coating Process

The following carbon samples were used for the experiments:

1. Ensaco 25 Og: conductive carbon black

2. E-MM131: graphitized E-250g

3. EP-P434: fullerenic carbon black with precursor E-250g

4. KS 4: primary synthetic graphite

5. RP-P534: fullerenic graphite

Ensaco 250 and KS4 were commercially available products of Timcal S.A.E-MM-131, EP 434 and RP534 were experimental products of Timcal S.A.

The detailed process conditions for the treatment of the above carbontypes in the radio frequency (RF) plasma vertical reactor are given inTable I. The plasma vertical reactor was of the size and type as shownin FIG. 4.

TABLE I Experimental conditions for the plasma polymerization process.Acetylene concentration Treatment time Sample Code RF Power (watts)(milliTorr) (hrs) E-250 250 200 1 E-MM131 250 200 1 EP-P434 250 200 1 KS4 250 200 1 RP-P534 250 200 1 EP-P434-5 150 200 1Characterization of the Samplesa. Thermogravimetric Analysis

A Perkin Elmer TGA was used for thermogravimetric analysis of thesamples. The samples were heated from 50° C. to 800° C. at 10° C./min inan air atmosphere. The thermal degradation behavior of pure plasmapolymerized acetylene was first studied. Pure plasma polymerizedacetylene starts decomposing at 265° C. and the decomposition iscomplete at 600° C. Based on this observation, the weight losses for thecoated and uncoated fullerenic soots were calculated in theaforementioned region of decomposition of said plasma polymerizedacetylene. The difference in weight loss between the coated and uncoatedsamples corresponds to the amount of plasma polymerized acetylene formedon its surface.

The TGA thermograms of various carbon black samples are shown in FIGS.5A-5F. Calculated weight losses for each sample are shown in Table II.Among the different samples, fullerenic soot E-P434 gave high amount ofdeposition of plasma polymerized acetylene. The fullerenic graphiteRP-P534 did not show appreciably high deposition than its precursor, theprimary synthetic graphite KS 4. However, the graphitic samples showed asomewhat higher deposition than the E-250g and EM-M131.

The fullerenic soot E-P434 gave also high deposition under a differentprocess condition.

TABLE II Calculated weight losses for various plasma coated samplesSample Weight loss (%) E-250g Ac 2.3 E-MM131-Ac 1.8 E-P434-Ac 14.0 KS4-Ac 3.1 RP-P534-Ac 3.4 E-P434 Ac-5 12.2b. X-Ray Photoelectron Spectroscopy

Surface analysis was performed on a Quantera XPS from PhysicalElectronics equipped with an Al Kα X-ray source (1486.6 eV). The spectrawere obtained with pass energy of 224 eV and the elemental scans wereacquired at 55 eV and 0.1 eV stepwise.

The concentration of carbon and oxygen on the surface of fillers beforeand after modification is shown in Table III.

TABLE III Elemental concentration on various samples Sample C % O %E-250g 98.81 1.19 E-250g-Ac 96.95 3.05 E-MM131 98.46 1.54 E-MM131-Ac96.58 3.42 E-P434 97.36 2.64 E-P434-Ac 92.62 7.38c. Surface Area Measurements

The BET surface area and CTAB surface area of the fullerenic soot beforeand after modification was measured. After the deposition of theacetylene plasma polymer, the BET as well as CTAB surface area werefound to be decreased. Results are shown in Table IV.

TABLE IV Surface areas of treated and untreated fullerenic soot. BETNitrogen surface area CTAB surface area Sample (m²/g) (m²/g) E-P434 69.872 E-P434-Ac 637 61d. Transmission Electron Microscopy.

The carbon particles of the sample E-P434 were subjected to TEM imagingbefore and after treatment according to the conditions specified inTable 1. It can be seen that the thickness of the coating was in therange of 3-5 nm in most areas of the core particles, and in some areasit extended up to a range of 7-9 nm.

Conclusion:

The surface of fullerenic soot E-P434 can be readily modified bydepositing a plasma polymerized acetylene layer through plasmapolymerization. The thickness of the layer formed on the surface is inthe range of about 5 nm.

Example 2: Surface Energy of Treated and Untreated Carbon Black

Non-fullerenic furnace carbon black (N330) was subjected to treatmentwith acetylene plasma for one and four hours, respectively (N330). Thesurface energy of treated samples was compared to fullerenic sootparticles treated for one hour in an acetylene plasma. The results ofsolvent immersion tests are depicted in the Scheme below:

Thus, the coated carbon black shows appreciable reduction in surfaceenergy. The modified fullerene soot after 1 hr treatment showed surfaceenergy reduction similar to a 4 hr treated furnace carbon black (N330).

Example 3: Plasma Coated Fullerenic Soot for Use in Polymer Blends

The fullerenic soot in the fluffy form was obtained from Timcal Graphiteand Carbon, Belgium. The sample code was RP-P579. The BET specificsurface area of the fullerenic soot was 66.8 m²/g. The monomer used forplasma polymerization was acetylene (99.6% purity) as supplied byMatheson Trigas, Ohio, USA.

The rubbers used for the experiments were a solution ofStyrene-Butadiene-Rubber (S-SBR), Acrylonitrile-Butadiene-Rubber (NBR)and an Ethylene-Propylene-Diene rubber (EPDM). S-SBR was supplied byLanxess Corporation, Germany: Buna VSL 5025-OHM with Mooney viscosity ML(1+4)100°) C.: 65, vinyl content 50 wt %, styrene content 25 wt %. NBRwas also supplied by Lanxess Corporation, Germany: Perbunan NT 3446 withMooney viscosity ML (1+4)100° C.: 45, acrylonitrile content 34.7±1 wt %.EPDM rubber was supplied by DSM Elastomers B.V. the Netherlands: Keltan4703 with Mooney viscosity ML (1+4)125° C.: 65, ethylene content 48 wt %and ethylidene norbornene content 9.0 wt %.

Rubber compounds with fullerenic soot are denoted as FS and those withthe plasma-coated fullerenic soot are denoted as PCFS.

Plasma polymerization was carried out in a Radio-frequency (RF) plasmatumbler reactor. After introduction of 100g of fullerenic soot, thechamber was evacuated to a pressure of 10 Pa. Then monomer was injectedinto the reaction chamber under steady flow conditions, maintaining apre-determined monomer pressure inside the chamber. SubsequentlyRE-power was applied. A frequency of 13.56 MHz was applied. Theconditions of the process were varied as given in Table V, in order tofind an optimized condition for the process based on the amount ofplasma-polymer deposited on the surface of the soot.

TABLE V Experimental Conditions Employed for the Plasma Polymerizationonto Fullerenic Soot Monomer RF Power Concentration Treatment TGA weightSample Code (Watts) (Pa) Time (hr) loss (%) RP-P579-1 80 20 1 1.72RP-P579-2 100 40 1 2.15 RP-P579-3 100 40 2 4.01 RP-P579-4 100 50 2 3.9RP-P579-5 100 50 2.5 5.06 RP-P579-6 100 40 2.5 5.5Resistivity of Plasma Coated Fullerenic Soot Samples

The resistivity of plasma coated versus uncoated fullerenic soot samplesis depicted in FIG. 6. It can be derived from the data shown in theFigure that the resistivity of fluffy fullerenic soot increasessubstantially after the deposition of plasma coating. This directlytranslates to less carbon-carbon contacts in the plasma-coated state.For application in rubber, the fluffy fullerenic soot was granulated.The conductivity measurements carried out on the granulated sample alsoshow an increased resistivity relative to the uncoated version. Comparedto the fluffy plasma-coated fullerenic soot, there is some reduction inresistivity, especially at higher compacted densities. Still, theresistivity values are substantially higher than observed for theuncoated version. This means that even after granulation there is stilla significant amount of plasma coating on the surface of fullerenicsoot, indicating a good adherence of the coating. In other words, bycoating fullerenic soot through plasma polymerization a significantincrease in resistivity of the resulting composition is observed.

Rubber Mixing and Curing

Rubber compounds with fullerenic soot samples were prepared according tothe formulations given in Table VI below. The mixing was carried out ina Brabender Plasticorder internal mixer with a chamber volume of 390 ml.The mixing procedure employed is mentioned in Table VII. The startingtemperature was 50° C. The mixing conditions were optimized to obtain amixing energy smaller than 500 MJ/m³. This was done to obtain asituation comparable with that of industrial scale mixing. The rotorspeed was 50 rpm. After mixing, the compound was discharged and wassheeted out on a two roll mill. The addition of sulfur and acceleratorswas carried out on a two roll mill as well.

After the addition of curatives, the curing properties of the compoundwere determined using a RPA 2000 from Alpha Technologies. The optimumvulcanization time t₉₀ and scorch time t₉₂ were determined. Thecompounds were subsequently cured in a Wickert laboratory press at 160°C. and 100 bar pressure.

TABLE VI Compound Formulations in phr Component SBR, NBR or 100 100 100EPDM Carbon black 20 30 40 Zinc oxide 4 4 4 Stearic acid 2 2 2 TMQ 1 1 1Sulphur 2.5 2.5 2.5 CBS 1.98 1.98 1.98 TOTAL 131.5 141.5 151.5

TABLE VII Mixing Scheme Time (min) Action 0.0  Open ram, add rubber0.00-1.30 Rubber mixing 1.30-2.10 Add ZnO, stearic acid, TMQ, and ½fullerenic soot 2.10-3.10 Mixing 3.10-3.50 Add ½ fullerenic soot3.50-5.50 Mixing 5.50 DumpResultsBehavior of Plasma Coated Fullerenic Soot in Rubber

As described above, plasma coated fullerenic soot was mixed with thedifferent rubbers SBR, NBR and EPDM. The mixing energy was optimized tobe smaller than 500 MJ/m³. Strain sweep measurements of uncuredcompounds were performed on the RPA 2000. The storage modulus wasmeasured in the range of 0.56%-100.04% strain. The temperature andfrequency were kept constant at 60° C. and 0.5 Hz.

The Payne effects of the plasma coated fullerenic soot filler at variousfiller loadings in SBR, NBR and EPDM are shown in FIGS. 7 to 10,respectively. The difference in G′ value at 0.56% strain and 100.04%strain can be represented as the Payne effect. The Payne effect isusually used to obtain information regarding the filler-fillerinteraction in a rubber matrix. The higher the storage modulus (G′)value at lower strains, the higher is the filler-filler interaction.During the strain sweep measurement, the storage modulus value decreasesdue to breakdown of the filler-filler network to obtain similar G′values at high strains, irrespective of the filler-filler interaction tobegin with at low strain.

The Payne effect is usually employed for rubber compounds with fillercontents above the percolation threshold, which is—depending on thespecific grade of carbon black—usually in the range of 30 phr (parts perhundred of rubber). The plasma coated fullerenic soot shows a lowerPayne effect in all rubber compounds and at all filler concentrations.The difference in Payne effect value becomes more prominent at higherfiller loadings. The relative decrease of the Payne effect in differentrubbers is demonstrated in FIG. 10. It clearly shows that at lowerfiller loadings (20 and 30 phr), the decrease of the Payne effect ismost prominent in EPDM rubber. But at higher filler loadings the effectis almost the same for the other rubber samples tested.

The stress-strain properties of the cured compounds with the carbonblack samples were measured according to ISO 037. The measurements werecarried out on a Zwick Z 1.0/TH 1 S tensile tester. The stress-straincurves of vulcanisates of SBR, NBR and EPDM with 40 phr filler loadingare shown in FIGS. 11-13, respectively. SBR with plasma-coatedfullerenic soot showed a slight improvement in tensile strength. In thecase of NBR, no significant improvement was observed. In the case ofEPDM, there is an appreciable reduction in tensile strength, accompaniedby an improvement in elongation at break.

Carbon black can interact chemically and physically with elastomers andthus contribute to the reinforcement of the elastomer. It is widelyaccepted to use the carbon black-rubber interaction parameter to denoteand quantify the interaction between rubber and carbon black. It iscommonly referred to as the slope of the stress-strain curve in arelatively linear region, typically within the range of extension ratiosfrom 100 to 300%

-   -   Carbon black-rubber interaction parameter

$\sigma = \frac{\sigma_{b} - \sigma_{a}}{\lambda_{b} - \lambda_{a}}$

Where σ_(b) and σ_(a) are the stresses at corresponding strains λ_(b)and λ_(a): 300 and 100, respectively. The modulus development at theseelongations has been shown to depend on strong adhesion between thecarbon black surface and the polymer. While comparing different carbonblacks, the slope of the stress strain curve was found to be a betterindicator of the polymer-filler interaction than the individual modulusvalues.

The calculated σ-values are tabulated in Table VIII. In the case of SBRand NBR a slight increase in σ-value was observed, whereas in the caseof EPDM a significant reduction in carbon black-rubber interaction wasobserved.

TABLE VIII Carbon black-rubber interaction parameter for differentsystem Sample FS PCFS SBR 5.5 5.8 NBR 7.5 7.8 EPDM 8.5 5.8

The invention claimed is:
 1. A process for producing an active fillercomprising: providing carbon residue particles comprising fullerene-typenanostructures; and plasma polymerizing a monomer on the carbon residueparticles to produce an active filler suitable for use in rubber,wherein the carbon residue particles were produced by exposing a carbonprecursor selected from carbon black, graphite, expanded graphite andcombinations thereof to any one or more of: 1) a high temperature plasmatreatment; 2) a radio frequency plasma treatment; 3) combustion; 4) anarc process; or 5) laser ablation, and wherein the carbon residueparticles have carbon rings on carbon particle surfaces.
 2. The processof claim 1, wherein the plasma polymerizing is carried out in afluidized bed plasma polymerization reactor.
 3. The process of claim 1,wherein the thickness of a plasma polymer formed on the carbon residueis in the range of 3 nm to 9 nm.
 4. The process of claim 1, wherein aplasma polymer formed represent 1.0% to 30% of the mass of the activefiller.
 5. The process of claim 1, wherein a plasma polymer formedrepresents 1.5% to 20% of the mass of the active filler.
 6. The processof claim 1, wherein the carbon residue particles are produced by acombustion process, an arc process, or by laser ablation.
 7. The processof claim 1, wherein the monomer comprises a hydrocarbon monomer.
 8. Theprocess of claim 1, wherein the plasma polymer comprises at least onecarbon-carbon double bond.
 9. The process of claim 1, wherein the plasmapolymerization is carried out in less than 4 hours.
 10. The process ofclaim 1, wherein the plasma polymerizing of the monomer produces a layerof plasma polymer having a lower surface energy than the surface energyof the carbon particle.
 11. The process of claim 10, wherein the surfaceenergy is less than 65.0 mJ/m2.
 12. The process of claim 10, wherein thesurface energy is less than 60.0 mJ/m2.
 13. The process of claim 10,wherein the thickness of the layer of plasma polymer formed on thecarbon particle is in the range of 3 nm to 9 nm.
 14. The process ofclaim 10, wherein a plasma polymer formed represents 1.0% to 30% of themass of the carbon particle.
 15. A process for producing a polymericcomposition comprising: providing an active filler comprising carbonresidue particles and a plasma polymer adjacent to a surface of thecarbon residue particles having carbon rings; and incorporating theactive filler into one or more polymers, wherein the carbon residueparticles were produced by exposing a carbon precursor selected fromcarbon black, graphite, expanded graphite and combinations thereof toany one or more of: 1) a high temperature plasma treatment; 2) a radiofrequency plasma treatment; 3) combustion; 4) an arc process; or 5)laser ablation, and the carbon residue particles comprise fullerene-typenanostructures.
 16. The process of claim 15, wherein the polymer is anatural or synthetic elastomer.
 17. The process of claim 15, wherein thepolymer is selected from the group consisting of natural rubber,styrene-butadiene-rubber, acrylonitrile-butadiene-rubber, orethylene-propylene-diene rubber.
 18. The process of claim 15,characterized in that ultimate resistivity is within a range between 103and 1013 Ohmcm.
 19. The process of claim 15, wherein the active filleris used to compatibilize polymers with low affinity to each other anddifferent affinity to the carbon filler.
 20. The process of claim 15,wherein the polymeric composition is a tire.